The acronym RFID is taken from the term “Radio-Frequency Identification.” With RFID, small electronic tags are programmed with identifying data or other information. RFID tags are capable of wirelessly providing information using a radio frequency (RF) communication channel. In one example usage scenario, an inventory product code such as a stock-keeping unit (SKU) may be stored by an RFID tag to track inventory in a warehouse or to facilitate customer check-out in a store. RFID tags can therefore be used instead of bar codes. Bar codes are visual identifiers that necessitate line-of-sight to be acquired by a bar code reader. RFID tags, in contrast, do not require a line-of-sight view for RFID readers to acquire information that is stored on the RFID tags.
For responsive RFID tags, an RFID reader transmits an interrogation signal that effectively serves as a broadcast message requesting RFID tags that are in range to return information that the RFID tags have stored. If multiple RFID tags are in range, then an RFID reader may be inundated with multiple responses from multiple RFID tags. Multiple responses confuse the RFID reader such that at least some of the responses are not correctly received or not correctly interpreted. The more RFID tags that are in range of an interrogation signal that is transmitted by an RFID reader, the greater the likelihood that responses sent by the RFID tags will create mutual interference due to colliding signals and the larger the probability that the RFID reader will fail to correctly receive or will fail to correctly interpret all of the responses sent by the RFID tags.
As production costs have decreased, RFID tags have become more common. Cheaper RFID tags may become ubiquitous in the coming years for inventory purposes as well as for many other usage scenarios. Consequently, problems with reading RFID tags due to collisions of multiple responsive signals will become increasingly prevalent. The frequency of occurrence of tag reading collisions can be ameliorated, to some degree, using purely electronic approaches. However, such purely electronic approaches increase the cost and complexity of RFID readers or RFID tags, and purely electronic approaches may not be wholly effective or may not be universally applicable across different manufacturers or RFID platforms.